1. Field of the Invention
The invention relates to nanosensors, and more particularly, to a method and device for detecting and quantifying charged molecules and favourably heavy metal ions in a fluid. The present invention advantageously applies to sewage sludge, but it could apply to biological or medical fields. It could also apply to the detection of other ionic species in fluid, not only heavy metal ions.
2. Description of the Related Art
The urban wastewater collection is one of the main facilities used for the disposal of commercial and domestic wastes, both of which may contain heavy metals. Wastewater treatment processes are generally effective in limiting the discharge of potentially toxic elements to the aquatic environment because a high proportion of the contaminant load is extracted and concentrated in the sewage sludge. Application of sewage sludge to agricultural land is the largest outlet for its beneficial use, and this is consistent with EC policy on waste recycling, recovery, and use. The Sewage Sludge Directive 86/278/EEC sets upper limits of trace metals in municipal sewage sludge for use on agricultural land, and revision of the directive is expected to lead to even more stringent limits. This is a critical issue due to the increasing amount of sludge produced (from 5.5M tonnes of dry matter in 1992 to 9M tonnes in 2005), and the fact that other alternatives (incineration and landfill) are not generally considered environmentally acceptable. Consequently, wastewater sludge quality must be protected and improved in order to secure the agricultural outlet as the most cost effective as sustainable solution.
The most widespread method for the determination of metal concentrations in wastewaters is via grab sampling and subsequent laboratory analysis. This method is both expensive, which limits its application, and time consuming, which means that pollution events can be missed, or detected too late. In the face of increasing levels of sludge production, the expected application of more stringent limits on heavy metal concentrations in sludge, and to identify, survey, and control the sources of input of toxic elements, there is a need for a low cost, time effective, easy to handle and very sensitive analysis system to determine the concentration of heavy metals in waste waters.
In addition, existing sensors to detect metal residues present following drawbacks:                metal-based screen-print electrodes or modified glassy carbon are not accurate enough to detect residue (detection limits of 0.5, 2.0, 0.9 and 1.4 μg/L),        most of them suffer from analyte peak distortion, peak overlap, and loss of sensitivity due to interference of analyte ions with each other,        Hg film coated electrodes are accurate enough at ppt levels (ng/L) by ion pre-concentration but not environmentally friendly.        